For mobile applications, e.g., automobiles, heat exchangers are used in various capacities to dissipate or absorb heat energy from a circulated fluid. For example, most conventional liquid cooled internal combustion engines include a radiator and a heater core for dissipating heat energy generated by the automotive engine.
Heater cores, in particular, are provided with a tubular inlet port centered along a flow axis for receiving high temperature fluid from a heat source, namely the automotive engine. An inlet tank having a predetermined height and a predetermined length and at least one wall spaced from the flow axis receives high temperature fluid from the inlet port. Hence, hot fluid from the engine enters the heater core through the inlet port and is directed immediately into an inlet tank. A plurality of flow tubes extend from the inlet tank for dissipating heat energy from the fluid. In this manner, the flow of high temperature fluid is divided among the various flow tubes and carried away from the inlet tank so as to dissipate heat energy from the fluid. An outlet tank is provided for receiving low temperature fluid from the various flow tubes. Therefore, the plurality of flow tubes all communicate with a common outlet tank and deliver low temperature fluid to the outlet tank to be returned to the heat source through a tubular outlet port extending from the outlet tank.
A major deficiency of the prior art heater cores is that the rate of fluid flow through the various flow tubes is highly nonuniform between the inlet tank and the outlet tank. That is, the velocity of coolant flow varies considerably from one flow tube to the next. This nonuniformity of flow causes a decrease in the overall thermal performance, i.e., heat dissipation, of the heat exchanger, and perhaps more importantly is the direct cause of accelerated erosion in the flow tubes.
The prior art as attempted to solve the erosion problem and nonuniform flow problem by staking a solid, sheet-like baffle plate within the inlet tank, perpendicular to the flow axis of the inlet port, to prevent impingement of the incoming fluid flow directly on the flow tubes adjacent the flow axis of the inlet port. In FIG. 1, such a prior art heater core is generally shown at 10 including the typical tubular inlet port 12, inlet tank 14, flow tubes 16, outlet tank 18, and outlet port 20. The baffle plate is generally indicated at 22 and shown disposed directly over at least one flow tube 16. Therefore, fluid flow entering the inlet tank 14 is directed away from the flow tube 16 directly beneath the baffle plate 22, thereby accelerating erosion in this flow tube 16, as well as any other flow tubes 16 which experience a diminished coolant flow rate due to the baffle plate 22, and, because the heater core 10 shown in FIG. 1 causes a significant nonuniformity in the flow rate of fluid through the various flow tubes 16, the thermal efficiency of the heater core 10 is retarded.
The highest fluid flow rate occurs in the flow tube or tubes 16 located adjacent the partition wall 24 dividing the inlet tank 14 and the outlet tank 18. This is because the high temperature fluid entering the inlet tank 14 strikes the staked-in baffle plate 22 directly in front of certain eclipsed flow tubes 16. This splits the incoming high temperature fluid flow into two streams of substantially equal momentum. As viewed from the drawing of FIG. 1, the stream directed toward the right contacts the partition wall 24 giving up its momentum upon impact. This results in a relatively high flow through the flow tubes 16 located adjacent the partition wall 24. The stream directed toward the left end wall 26 of the inlet tank 14, on the other hand, generally does not encounter such a momentum reducing obstruction because the left end wall 26 is shaped to more efficiently direct the flowing fluid into the adjacent flow tubes 16, thus resulting in a progressive reduction in the fluid flow momentum. Therefore, by the time the stream directed leftward of the baffle plate 22 impacts the left end wall 26, its momentum is not as high as that of the stream directed rightwardly toward the partition wall 24. Consequently, the flow rate in the flow tubes 16 adjacent the left end wall 26 is not as high as that in the flow tubes 16 adjacent the partition wall 24. However, the flow rate in the flow tubes 16 directly adjacent the left end wall 26 is higher than the flows in the several next rightwardly adjacent flow tubes 16 due to the loss of momentum at the left end wall 26 which is translated into increased flow through the flow tubes 16 directly adjacent the left end wall 26.
Another prior art attempt to diminish the erosion problem is shown in U.S. Pat. No. 5,000,259 to Forrest, issued Mar. 19, 1991 and assigned to the assignee of the subject invention. The Forrest patent discloses a heater core having a greater number of tubes in the inlet pass than in the outlet pass. Thus, the overall velocity of coolant flow through the inlet tubes is reduced with an accompanying decline in the rate of inlet tube erosion. However, the overall velocity through the outlet tubes is higher than that through the inlet tubes leading to non-uniform erosion of tubes. Although effective, this method is costly in high production quantities and somewhat sacrificial of thermal transfer performance.
Hence, an improved heater core construction is needed wherein the flow rate through the various flow tubes 16 is more closely patterned to an ideal equivalent flow rate among the various flow tubes 16 so that the overall thermal performance may be enhanced and the occurrence of erosion reduced.